How do I interpret the results of a DFT?

I have RF data that I would like to model with an equation. The graph looks like it might fit into a periodic function very nicely because it resembles a sine/cosine wave and has a period of exactly one day. Using the program ROOT, I am able to perform the fast Fourier transform algorithm on the data. The result is several histograms that look something like http://root.cern.ch/root/html/tutorials/fft/FFT.C_0.png" [Broken]. I have a histogram of the magnitude, phase, real part, and imaginary past of the transform. However, I am not sure how to use those histograms to reconstruct on original equation as the sum of sinusoids. Can you help me understand how to do this, or point me to somewhere where I can learn?